Bell's theorem

John Stewart Bell proved that no physical theory based on local hidden variables can ever reproduce all the predictions of quantum mechanics. His theorem established that quantum entanglement features non-local correlations stronger than classical physics allows.

The Bell inequality is a mathematical limit on the degree of correlation between measurements that can occur in any local realistic theory. Quantum mechanics routinely violates these inequalities, proving that entangled particles share a connection that transcends space.

Physicists Alain Aspect, John Clauser, and Anton Zeilinger conducted definitive experiments in the 1980s and beyond, measuring entangled photons. Their results definitively violated Bell's inequalities, confirming quantum non-locality and earning them the 2022 Nobel Prize in Physics.

Local hidden variables are pre-existing properties or instructions that particles possess before they are measured, an idea championed by Albert Einstein. Bell's theorem ultimately disproved the viability of these variables as an explanation for quantum phenomena.